package org.apache.lucene.index;

/**
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

/** TermDocs provides an interface for enumerating &lt;document, frequency&gt;
 pairs for a term.  <p> The document portion names each document containing
 the term.  Documents are indicated by number.  The frequency portion gives
 the number of times the term occurred in each document.  <p> The pairs are
 ordered by document number.

 @see IndexReader#termDocs()
 */

public interface TermDocs {
    /** Sets this to the data for a term.
     * The enumeration is reset to the start of the data for this term.
     */
    void seek(Term term) throws IOException;

    /** Sets this to the data for the current term in a {@link TermEnum}.
     * This may be optimized in some implementations.
     */
    void seek(TermEnum termEnum) throws IOException;

    /** Returns the current document number.  <p> This is invalid until {@link
     #next()} is called for the first time.*/
    int doc();

    /** Returns the frequency of the term within the current document.  <p> This
     is invalid until {@link #next()} is called for the first time.*/
    int freq();

    /** Moves to the next pair in the enumeration.  <p> Returns true iff there is
     such a next pair in the enumeration. */
    boolean next() throws IOException;

    /** Attempts to read multiple entries from the enumeration, up to length of
     * <i>docs</i>.  Document numbers are stored in <i>docs</i>, and term
     * frequencies are stored in <i>freqs</i>.  The <i>freqs</i> array must be as
     * long as the <i>docs</i> array.
     *
     * <p>Returns the number of entries read.  Zero is only returned when the
     * stream has been exhausted.  */
    int read(int[] docs, int[] freqs) throws IOException;

    /** Skips entries to the first beyond the current whose document number is
     * greater than or equal to <i>target</i>. <p>Returns true iff there is such
     * an entry.  <p>Behaves as if written: <pre>
     *   boolean skipTo(int target) {
     *     do {
     *       if (!next())
     * 	     return false;
     *     } while (target > doc());
     *     return true;
     *   }
     * </pre>
     * Some implementations are considerably more efficient than that.
     */
    boolean skipTo(int target) throws IOException;

    /** Frees associated resources. */
    void close() throws IOException;
}
